This invention relates to voice-triggered switching and more particularly to a method and apparatus for producing a speech indication signal in response to detection of voice information in the presence of extreme spurious background signals. A voice operated switch is useful for voice-triggered control of equipment such as telephone and radio transmitters as well as an element of a speech enhancement apparatus requiring separation of time frames containing speech from time frames containing undesired audio information in extremely noisy environments.
Prior voice operated switches have employed various techniques and primarily analog signal detection techniques.
Poikela U.S. Pat. No. 4,625,083 describes a two-microphone voice-operated switch (VOX) system which seems to suggest autocorrelation of signals in an analog sense through the use of a differential amplifier for comparing the signals from the two microphones. This technique is reminiscent of noise cancellation microphone techniques and is not particularly pertinent to the present invention.
Mai et al. U.S. Pat. No. 4,484,344 is a syllabic rate filter-based voice operated switch. It employs input signal conditioning through an analog low-pass filter to limit examination of signal content to below 750 Hz.
Luhowy U.S. Pat. No. 4,187,396 describes an analog voice detector circuit employing a syllabic rate filter. It uses a hangover time function operative as an envelope detector.
Jankowski U.S. Pat. No. 4,052,568 describes a digital voice switch using a digital speech detector and a noise detector operating on broad spectrum speech signals. It also teaches the hangover time function and dual threshold detection.
Sciulli U.S. Pat. No. 3,832,491 describes an early digital voice switch wherein a digital adaptive threshold is employed based on the number of times the amplitude of talker activity exceeds an amplitude threshold per unit time.